This invention relates to door mechanisms, and more particularly to counterbalancing springs for heavy doors such as found in garages and the like.
Many car garages, expecially those in residential buildings, are equipped with doors that are opened by raising them from a vertical closed position to a horizontal open position. The doors, which are quite heavy, must be counterbalanced to permit reasonably easy opening and closing.
The garage doors of the prior art, whether directly pivoted on a horizontal axis or raised by a linkage mechanism, are usually conterbalanced by long, helical, closely wound tension springs.
There are several disadvantages with the conventional tension springs of the prior art. Tension springs are not very durable. They break after a certain amount of use as a result of overloading and/or metal fatigue. The breakage occurs usually while the spring is extended from the relatively relaxed open position as the door is closed. The danger of spring breakage is aggravated by the presence of adjustment devices in most prior art door mechanisms. In an effort to increase the counterbalancing force, the spring can be adjusted to a greater extension than it can safely stand, becoming overloaded when the door is closed. When breakage occurs, pieces and small metal fragments from the broken spring can fly through air, posing a serious danger to both life and property. The end portions of the broken spring can whip around, presenting additional dangers. Also, if the spring breaks while the door is being lifted or lowered, the loss of the counterbalancing tension provided by the spring can cause the door to come crashing down, again posing grave health hazards to a person operating the door.
Moreover, most garage door spring assemblies use helical tension springs with unsightly exposed coils. The coils separate when the spring is extended. There is always the danger that objects or fingers can be caught between the coils when tension is relaxed, causing damage or physical injury.
Thus there is a need for a door counterbalancing spring that is safe and reliable, inexpensive to make and install, neat in appearance, and capable of replacing conventional springs in existing installations.